When a watch is registered, a new document that represents the watch is added to
the .watches index and its trigger is immediately registered with the relevant
trigger engine. Typically for the schedule trigger, the scheduler is the
trigger engine.

Putting a watch must be done via this API only. Do not put a watch
directly to the .watches index using the Elasticsearch Index API.
If X-Pack security is enabled, make sure no write privileges are
granted to anyone over the .watches index.

When adding a watch you can also define its initial
active state. You do that
by setting the active parameter.

When X-Pack security is enabled, your watch will only be able to index or search on
indices for which the user that stored the watch, has privileges. If the user is
able to read index a, but not index b, the same will apply, when the watch
is executed.